The spinal cord exhibits motor function after all neuronal connections with supraspinal structures are severed. Our work contributes to spinal motor neurophysiology by examining the neuronal mechanisms responsible for the production of three types of scratch reflexes in the spinal turtle. The sequences of motor neuron activity patterns characteristic of each type of scratch are produced in a spinal turtle immobilized with neuromuscular blockade. This preparation has the mechanical stability to allow intracellular recordings from spinal cord neurons during the production of scratch reflex motor activity. We will characterize the excitatory and inhibitory synaptic potentials in motor neurons during the three forms of the scratch reflex using intracellular recording techniques. We will use these data to predict the timing characteristics of spinal interneurons generating the scratch reflex. We will examine the activity patterns of spinal interneurons directly during these reflexes using both intracellular and extracellular recording techniques. We will examine restricted preparations consisting of two to four segments of the spinal cord that are capable of producing scratch motor patterns. We will use these data to determine the segmental locations of the interneurons generating each of the forms of the scratch reflex. We will develop in vitro preparations using these restricted portions of the spinal cord suitable for pharmacological manipulations of the generator network. We will use our PDP-11/23+ computer to analyze the motor patterns during the scratch and will develop graphical techniques for computer pattern recognition of the scratch motor patterns. We will study blends of several forms of the scratch reflex that are produced by simultaneous stimulation of two sites on the body surface in order to determine the rules of selection and interruption of motor programs. We will use our data to test a set of working hypotheses concerning the interneuronal organization of spinal cord motor pattern generators. Since the spinal cord of humans is similar to that of the lower vertebrates, our work will serve as useful working hypotheses for those currently developing neural motor prostheses for spinal-injured humans.